This invention claims the benefit of Japanese Patent Application No. HEI 11-361125, filed on Dec. 20, 1999, which is incorporated by reference.
1. Field of the Invention
The present invention relates to an electro-photographic photoconductor where energy of a most outer surface of the photoconductor is defined, and more particularly to a configuration where the energy of the most outer surface e.g. a surface protection layer is determined so that dramatically superior images can be obtained by copiers in which such photoconductors are used while both conserving energy and prolonging life-span of such photoconductors.
2. Description of Related Art
FIG. 2 shows an example of a conventional configuration of electro-photographic photoconductor 90 comprising a conductive substrate 91 which is normally an aluminum cylinder, a carrier blocking layer 92 made of a material constituted mainly of silicon, a photosensitive layer 93, also made of a material constituted mainly of silicon, and a surface protection film 94. In many cases, the conductive substrate 91 is formed to be a circle of the cylinder.
The conductive substrate 91 is a base material of the photoconductor 90 on which layers 92, 93 and 94 are formed. The carrier blocking layer 92 prevents carriers from being injected from the conductive substrate 91. The photosensitive layer 93 mainly functions as a photoconductor. When the photosensitive layer 93 receives light, it liberates electron and positive hole pairs, and the electrons moves toward a most outer surface of the photoconductor 90. The surface protection film 94 is provided to make the photosensitive layer 93 resistant to moisture, abrasion and oxidation.
An aluminum cylindrical substrate is provided when the photoconductor 90 is used as an electro-photographic photoconductor in a copier. The surface of the photoconductor 90 is charged to approximately 100,000 volts/cm by a corona discharge etc. The surface of the photoconductor 90 is then exposed to light corresponding to characters or pictures it is desired to copy (surface charge disappears only at portions other than for the characters or pictures it is desired to copy). When toner is then applied to the photoconductor 90, this toner will only become attached to areas where surface charge remains. The toner is then transferred and fixed to a paper so as to provide a copy. Then, surface charge of the photoconductor 90 is removed, the surface of the photoconductor 90 is cleaned, and again can be charged and exposed repeatedly for use in other cycles of copying. This process is well known in the copier industry.
Silicon is given as the main material of the carrier blocking layer 92 and photosensitive layer 93 in the above description. However, other materials such as amorphous materials consisting mainly of amorphous silicon or selenium alloy or so-called OPC""s comprising mainly of organic material also may be used as known to a person skilled in the art.
When silicon is used as the main material in an electro-photographic photoconductor 90 of the related configuration, the photoconductor 90 has a long lifetime, because a surface of the photoconductor 90 has high hardness resulting in resistance to peeling-off, wear and abrasion. However, NOx filming occurs when toner is blown to the photoconductor 90, and also when the photoconductor 90 is charged by corona discharge (xe2x80x9cFilmingxe2x80x9d is a phenomenon an oxide film is generated on a metal surface). The filming is a major reason of resistance decrease of the most outer surface of the photoconductor 90. Surface charge leaks in a lateral direction (i.e. along the surface), and causes resolution decrease. And if the surface charge leaks proceed, blurring or running of the image may occur when an inage is made, and image quality may deteriorate dramatically.
The deterioration of image quality is caused by decrease of ability of the photoconductor 90 to charge. The ability to charge on itself is a major characteristic of a photoconductor. Generally speaking, when charging is carried out to 100,000 volts/cm at the photoconductor surface, a dark resistance of 1014 to 1015 xcexa9xc2x7cm is required. However, the oxide film causes this dark resistance to decrease, causing deterioration of image quality.
As a countermeasure for preventing formation of NOx film, when the photoconductor 90 is composed mainly of silicon, the photoconductor 90 is used under heating with temperature of 35-45 degrees. However, adding an apparatus to provide the heating increases the cost of the image-forming device such as a copier which incorporates the photoconductor 90. Power consumption is also increased to provide this heating, and a space is required in the copier to install such a heating device.
In order to resolve the aforementioned problems with the related art, in the present invention there is provided a photoconductor comprising a carrier blocking layer and a photosensitive layer formed on a conductive substrate, characterized by that the carrier blocking layer and the photosensitive layer are formed of an amorphous film, and that the surface energy of the most outer surface of the photoconductor can be 20 [mN/cm] or less, a value of a polarized element of surface energy of the most outer surface of the photoconductor is 2 [mN/cm] or less, and that a surface protection layer may also be formed on the photosensitive layer.